Studies on heat shock induction and transgene expression in order to optimize the Flp/FRT recombinase system in apple (Malus × domestica Borkh.)

The concept of cisgenesis could become a promising approach in future apple breeding. However, cisgenesis depends on the availability of effective tools for the production of marker-free genetically modified (GM) plants. The development of such plants was recently shown to be possible using a heat shock inducible Flp/FRT recombinase based transformation system allowing the excision of the marker gene from the genome of GM apple plant tissue. The present study was aimed on improving the efficiency of this system by testing three different methods for heat treatment. Leaf tissue of GM apple plants was heat treated on wet filter paper, on regeneration medium, and in water, respectively. Lowest rates of tissue vitality and callus formation were obtained after heat treatment in water. After heat treatment on wet filter paper one marker-free shoot was obtained, but the rate of success was not comparable to results published in earlier studies. Molecular investigation of the Flp/FRT system in apple revealed the presence of non-spliced flp mRNA transcripts in most samples tested. This is assumed to be one possible reason for the low percentage of completely marker-free shoots using the present Flp/FRT system. © 2013 Springer Science+Business Media Dordrecht.